Maternal separation modifies behavioural and neuroendocrine responses to stress in CCR7 deficient mice

Alterations in immune function of various humoral and cellular factors, including chemokines, secondary to early stress may play a role in the enhanced vulnerability to psychiatric conditions in those with a history of childhood adversity. C57BL/6 (WT) mice and mice deficient for the chemokine receptor type 7 (CCR7(-/-)) were used to determine the effects of maternal separation on a range of behaviours and the biological stress response. Unpredictable maternal separation (MS) was conducted for 3h daily from postnatal day 1 to 14, with subsequent behavioural testing at 10 weeks of age. Corticosterone was quantified in 11-week-old mice. Maternally separated (MS) CCR7(-/-), but not WT mice, displayed reduced interest in social novelty compared to CCR7(-/-) naïve mice. Separated CCR7(-/-) mice also exhibited significantly lower serum corticosterone concentrations compared to non-separated mice. CCR7(-/-) mice spent less time in the centre during an open field test and more time in the closed arm of the elevated zero maze compared to their wild-type (WT) controls suggesting they were more anxious, however, no difference was observed between MS and control mice in either strain or test. Together these findings suggest that CCR7 is involved in mediating social behaviour and stress response following maternal separation, whereas other behaviours such as anxiety appear to be modified by CCR7 independent of maternal separation. The observed altered cell-mediated immune function possibly underlying the behavioural and neuroendocrine differences in CCR7(-/-) mice following maternal separation requires further investigation.